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Heifer liveweight at first mating and calving influences reproductive performance and milk production potential. Achieving liveweight targets is crucial; otherwise, first calving may delay, and fertility may decrease. Aim for 30%, 60%, and 90% of mature weight at 6, 15, and 22 months, respectively. Regular weight checks ensure heifers meet targets, allowing for adjustments if necessary. Weight-for-age targets help assess herd progress. Three methods to estimate mature liveweight include liveweight breeding value, weighing mature cows, and using breed averages. Liveweight targets assist in farm management decisions, highlighting potential challenges and informing actions like supplement use and stocking rates.
Liveweight at first mating and calving will have an impact on the reproductive performance and milk production potential of heifers.
Heifers must be reared to achieve their liveweight targets otherwise their first calving will be delayed, liveweight at calving will be too low and fertility during the next mating period reduced. Well-grown heifers will produce more milk in the first lactation, compete better with mature cows and survive longer in the herd.
Having targets offers a measure of performance and indicates well-grown stock. Targets also establish an agreed position for farmers involved in a contract grazing relationship.
Because body weight is the key driver of puberty it is important that heifers reach key liveweight targets if they are going to reach puberty at 12 months and get in-calf at 15 months.
Achieving the 30-60-90 percentage targets is more important than the pattern of growth.
There are three methods to estimate average mature liveweights for a group of heifers: liveweight breeding value, weighing a selection of mature cows (6-8 years of age), and using a breed-based average mature weight.
Obtain a 'breeding value trait report' from your herd recording provider (e.g. CRV, LIC). From this report calculate the average Lwt BV using the following equation:
Mature liveweight = 503kg ± Lwt BV
|Objective measure||An on farm study showed that 30% of animals were not matched to the correct mother|
|Best prediction based on an animal’s genetics||Genes are randomly inherited|
|Based on actual data from sire proving herds||Normal variation is -5% to +5% of the prediction|
|Accounts for current breeding program targets||Liveweight is 35% heritable so management has more influence on the final result|
|Majority of animals will have a Lwt BV||Currently only available through MINDA software|
|Data will not be available for herds with a high proportion of overseas genetics|
Average herd liveweight can be determined by weighing a cross section of the mature herd. Weighing guidelines to establish the target are:
This information can be used to validate Lwt BVs and will be most accurate for herds with consistent breeding strategies and limited breed variation within the herd.
|Representative of actual herd||Time required|
|Data will not be available for herds with a high proportion of overseas genetics||Not every animal will represent “average”|
|Improves information for the herd (e.g. stocking rates, drench rates, mineral dosing)||Does not capture recent changes in breeding policies (e.g. increasing crossbreeding)|
|Captures management and environmental conditions of the farm system||Will set targets too low if mature stock were poorly grown|
Estimate the likely average mature weight from an assessment of the breed composition of the group of heifers using the table below
Source: National Dairy Statistics (2014)
As these mature weights are the average of the population, groups of heifers of a comparative breed can have targets above the average mature weight. Weight gain records and physical observations should also be used to evaluate the average mature weight when applied to a group of heifers. Based on base cow liveweight of 503kg.
Weight for age targets should be used for mobs. The average weight of a mob should meet each target weight-for-age, this will indicate that they are on track for meeting the 22-month target.
Individual heifer weights will fall on either side of the weight-for-age target. It is natural to have variation in a mob, and studies have shown that some healthy heifers may be 15% lighter than their peers.
Breed average mature liveweights and weight-for-age targets
Weight-for-age targets (highlighted) for animals of different mature liveweights, with guide weights for other ages.
|Mature weight||Age||Liveweight (kg)|
|100%||6 - 8 yrs||420||465||500||550||600|
Before heifers move properties, the group should meet their target weight-for-age. The number of animals below target and/or the range around the target should be documented, particularly in contract grazing situations.
Most dairy farmers and farm advisers can recognise whether heifers are in good or poor condition, but few can judge whether heifers have actually achieved target liveweights for their particular age.
Weighing heifers on a regular basis provides an 'accurate' assessment of how well heifers are growing compared to targets. It also allows for proactive management - if heifers are under target at weighing, remedial action can be taken to get them back on track. Find out more about heifer feeding and nutrition.
There is no strict rule about how often heifers should be weighed (InCalf recommends every 3 months). The more frequently heifers are weighed the more quickly a problem will be detected. Find out more about heifer weights and weighing.
Establishing heifer liveweight targets, and the growth required to meet them will aid farm management decision-making. The information can be used when answering a range of questions, including:
Liveweight targets can give you a better understanding of what the cost of growing heifers is going to be, which can then be used to assess the costs and benefits of using land for heifer grazing, to decide whether to purchase or lease land and to negotiate a fair price. They are a valuable tool to use when reviewing heifer management. Final weights can be compared with targets to identify missed opportunities and review costs. Targets can also be used to set minimum weights, establish rejection criteria, or prompt early culling.